U.S. patent application number 17/207475 was filed with the patent office on 2021-07-08 for systems and methods for adjusting fueling in a cylinder with a pre-chamber.
The applicant listed for this patent is Ford Global Technologies, LLC. Invention is credited to Chris Paul Glugla.
Application Number | 20210207551 17/207475 |
Document ID | / |
Family ID | 1000005466278 |
Filed Date | 2021-07-08 |
United States Patent
Application |
20210207551 |
Kind Code |
A1 |
Glugla; Chris Paul |
July 8, 2021 |
SYSTEMS AND METHODS FOR ADJUSTING FUELING IN A CYLINDER WITH A
PRE-CHAMBER
Abstract
Methods and systems are provided for operating a cylinder of an
engine including a pre-chamber ignition system. In one example, a
method may include determining amounts of pre-chamber gases in the
cylinder prior to combustion, and adjusting an amount of fuel
injected into the cylinder based on the amounts of pre-chamber
gases in the cylinder. In this way, cylinder fueling may be
compensated for additional air and/or fuel from the pre-chamber
gases, which may increase an accuracy of the cylinder fueling and
increase cylinder efficiency.
Inventors: |
Glugla; Chris Paul; (Macomb,
MI) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Ford Global Technologies, LLC |
Dearborn |
MI |
US |
|
|
Family ID: |
1000005466278 |
Appl. No.: |
17/207475 |
Filed: |
March 19, 2021 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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16719726 |
Dec 18, 2019 |
10989129 |
|
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17207475 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F02D 41/008 20130101;
F02D 41/3836 20130101; F02F 11/00 20130101; F02F 7/0002 20130101;
F02F 1/22 20130101; F02D 41/182 20130101 |
International
Class: |
F02D 41/18 20060101
F02D041/18; F02F 1/22 20060101 F02F001/22; F02D 41/38 20060101
F02D041/38; F02D 41/00 20060101 F02D041/00; F02F 7/00 20060101
F02F007/00; F02F 11/00 20060101 F02F011/00 |
Claims
1. A method, comprising: adjusting a fuel injection amount to a
cylinder based on an amount of pre-chamber gases in the cylinder
during a compression stroke of the cylinder.
2. The method of claim 1, wherein the pre-chamber gases flow to the
cylinder from a pre-chamber coupled to the cylinder via an opening
in walls of the pre-chamber.
3. The method of claim 2, wherein the amount of pre-chamber gases
is determined based on a pressure difference between the
pre-chamber and the cylinder.
4. The method of claim 3, wherein the pressure difference between
the pre-chamber and the cylinder is determined based on an
injection pressure of the pre-chamber and a position of a piston
within the cylinder.
5. The method of claim 4, wherein the injection pressure of the
pre-chamber is greater than or equal to a peak pressure of the
cylinder.
6. The method of claim 1, wherein the amount of pre-chamber gases
includes one or more of an amount of pre-chamber air, an amount of
pre-chamber fuel, and an amount of pre-chamber combustion gases
from a previous combustion cycle.
7. The method of claim 6, wherein adjusting the fuel injection
amount to the cylinder includes increasing the fuel injection
amount to the cylinder as the amount of pre-chamber air in the
cylinder during the compression stroke increases.
8. The method of claim 6, wherein adjusting the fuel injection
amount to the cylinder includes decreasing the fuel injection
amount to the cylinder as the amount of pre-chamber fuel in the
cylinder during the compression stroke increases.
9. The method of claim 6, wherein adjusting the fuel injection
amount to the cylinder includes decreasing the fuel injection
amount to the cylinder as the amount of pre-chamber combustion
gases from the previous combustion cycle in the cylinder during the
compression stroke increases.
10. The method of claim 1, wherein adjusting the fuel injection
amount to the cylinder is further based on an amount of air
inducted into the cylinder through an intake valve of the
cylinder.
11-15. (canceled)
16. A system, comprising: an engine including a plurality of
cylinders, each cylinder including a cylinder fuel injector and a
pre-chamber of a pre-chamber ignition system; and a controller
storing executable instructions in non-transitory memory that, when
executed, cause the controller to: purge gases from the pre-chamber
to the corresponding cylinder; and adjust a fuel injection amount
of the cylinder fuel injector based on an amount and composition of
the gases purged from the pre-chamber.
17. The system of claim 16, wherein the pre-chamber includes an air
injector, a pre-chamber fuel injector, and a spark plug, and
wherein the composition of the gases purged from the pre-chamber
includes at least one of air, fuel, and exhaust gas from a previous
combustion in the pre-chamber.
18. The system of claim 17, wherein to adjust the fuel injection
amount of the cylinder fuel injector based on the amount and
composition of the gases, the controller includes further
instructions stored in non-transitory memory that, when executed,
cause the controller to: increase the fuel injection amount of the
cylinder fuel injector as a proportion of air in the gases purged
from the pre-chamber increases; decrease the fuel injection amount
of the cylinder fuel injector as a proportion of fuel in the gases
purged from the pre-chamber increases; and decrease the fuel
injection amount of the cylinder fuel injector as a proportion of
exhaust gas from the previous combustion in the pre-chamber in the
gases purged from the pre-chamber increases.
19. The system of claim 17, wherein to purge gases from the
pre-chamber to the corresponding cylinder, the controller includes
further instructions stored in non-transitory memory that, when
executed, cause the controller to: actuate the air injector during
a compression stroke of the cylinder at an injection pressure at or
above a peak pressure of the cylinder.
20. The system of claim 19, wherein the controller includes further
instructions stored in non-transitory memory that, when executed,
cause the controller to: determine the peak pressure of the
cylinder based on at least a temperature of the engine and engine
load.
Description
FIELD
[0001] The present description relates generally to methods and
systems for controlling a vehicle engine to determine cylinder
fueling in a cylinder with an active pre-chamber.
BACKGROUND/SUMMARY
[0002] An internal combustion engine combusts an air-fuel mixture
within cylinders to produce torque, which may be used to propel a
vehicle. In some such engines, an ignition source is used to ignite
the air-fuel mixture within each cylinder during a compression
stroke. For example, in traditional spark-ignition engines, each
cylinder includes a spark plug for directly igniting the air-fuel
mixture within the cylinder. In other examples, the air-fuel
mixture within the cylinder may be ignited by jets of hot gas and
flame from a pre-combustion chamber, referred to herein as a
"pre-chamber." The pre-chamber may be walled chamber located in the
clearance volume of the cylinder, and may include a spark plug, an
O.sub.2 or air injector, and a fuel injector. During engine
operation, a first air-fuel mixture is introduced into the
pre-chamber, and a second air-fuel mixture is introduced into the
cylinder. When ignition is requested, the spark plug in the
pre-chamber actuates, igniting the first air-fuel mixture. As the
first air-fuel mixture combusts, jets of flame and hot gas may exit
the pre-chamber and enter the cylinder via one or more holes in the
pre-chamber walls. These jets ignite the second air-fuel mixture in
the cylinder to produce torque. Residual gases from combusting the
first air-fuel mixture may be actively purged from the pre-chamber
to the cylinder by injecting air (or O.sub.2) into the pre-chamber,
providing fresh air for a subsequent pre-chamber combustion.
[0003] Pre-chamber ignition may offer performance and efficiency
benefits over a spark-ignition engine in some situations. For
example, a cylinder with pre-chamber ignition may operate with a
higher (e.g., leaner) air-fuel ratio (AFR) than a similar cylinder
of a spark-ignition engine, which may lead to lower fuel
consumption in the cylinder with pre-chamber ignition. In other
examples, a cylinder with pre-chamber ignition may produce more
power than a cylinder ignited by a spark plug due to an increased
burn rate in the cylinder, which may reduce an amount of time for
knocking combustion to occur and thereby allow ignition timing to
be advanced further toward maximum brake torque (MBT).
[0004] However, gases may flow from the pre-chamber to the cylinder
via the one or more holes in the pre-chamber walls, which may
affect the AFR of the cylinder. For example, air or O.sub.2 from
the active purging may flow from the pre-chamber to the cylinder,
such as when the pressure in the cylinder is lower than the
pressure in the pre-chamber, leading to a higher (e.g., leaner)
cylinder AFR than expected. As another example, the residual gases
from the pre-chamber may dilute the air in the cylinder. As still
another example, the residual gases from the pre-chamber may be
fuel-rich, which may result in a lower (e.g., richer) cylinder AFR
than expected. When the AFR of the cylinder is not accurately
controlled, vehicle emissions may increase.
[0005] The inventors herein have identified the above-mentioned
issues and have identified a method to at least partially address
them. In one example, a method comprises: adjusting a fuel
injection amount to a cylinder based on an amount of pre-chamber
gases in the cylinder during a compression stroke of the cylinder.
In this way, the cylinder fuel amount may be adjusted to compensate
for pre-chamber gases in the cylinder prior to combustion in order
to more accurately operate the cylinder at a desired AFR.
[0006] As one example, the pre-chamber gases may flow to the
cylinder from a pre-chamber coupled to the cylinder via an opening
in the walls of the pre-chamber, and the amount of pre-chamber
gases may be determined based on a pressure difference between the
pre-chamber and the cylinder. As an example, as a pressure of the
cylinder further decreases below a pressure of the pre-chamber, the
amount of pre-chamber gases in the cylinder may increase. This
pressure difference may be determined based on an injection
pressure of the pre-chamber and a position of a piston within the
cylinder. For example, the injection pressure of the pre-chamber
may be a pressure greater than or equal to a peak pressure of the
cylinder. Further, the amount of pre-chamber gases that flow into
the cylinder may include one or more of an amount of pre-chamber
air, an amount of pre-chamber fuel, and an amount of pre-chamber
combustion gases from a previous combustion cycle. As one example,
adjusting the fuel injection amount to the cylinder may include
decreasing the fuel injection amount to the cylinder as the amount
of pre-chamber combustion gases from the previous combustion cycle
increases, as the pre-chamber combustion gases may dilute a
cylinder air charge. As another example, adjusting the fuel
injection amount to the cylinder may include decreasing the fuel
injection amount to the cylinder as the amount of pre-chamber fuel
in the cylinder increases. Additionally or alternatively, adjusting
the fuel injection amount to the cylinder may include increasing
the fuel injection amount to the cylinder as the amount of
pre-chamber air in the cylinder during the compression stroke
increases. Adjusting the fuel injection amount to the cylinder may
be further based on an amount of air inducted into the cylinder
through an intake valve of the cylinder. As a result, cylinder
efficiency may be increased.
[0007] In this way, a fuel injection amount to a cylinder may be
adjusted based on an amount of pre-chamber gases in the cylinder
during a compression stroke of the cylinder. By adjusting the fuel
injection amount, cylinder fueling may be more accurate relative to
systems without compensation, which may increase a performance of
the cylinder. Further, by compensating the fuel injection amount
for the amount and composition of pre-chamber gases in the
cylinder, the controller may prevent the cylinder from operating at
a non-stoichiometric AFR, which may increase a fuel efficiency of
the vehicle and decrease vehicle emissions.
[0008] It should be understood that the summary above is provided
to introduce in simplified form a selection of concepts that are
further described in the detailed description. It is not meant to
identify key or essential features of the claimed subject matter,
the scope of which is defined uniquely by the claims that follow
the detailed description. Furthermore, the claimed subject matter
is not limited to implementations that solve any disadvantages
noted above or in any part of this disclosure.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] FIG. 1 shows a schematic depiction of a cylinder
configuration in an engine system of a vehicle.
[0010] FIG. 2 shows an example method for operating a pre-chamber
of a pre-chamber ignition system.
[0011] FIG. 3 shows an example method for determining cylinder
fueling based on pre-chamber purge and pre-chamber air
injection.
[0012] FIG. 4 shows an example graph of pressure in a cylinder
relative to position of a piston.
[0013] FIG. 5 shows a prophetic example timeline of operating a
pre-chamber and a cylinder with pre-chamber purging.
[0014] FIG. 6 shows a prophetic example timeline of operating a
cylinder with different cylinder fueling amounts based on relative
amounts of pre-chamber gases in the cylinder.
DETAILED DESCRIPTION
[0015] The following description relates to systems and methods for
determining a fueling amount for a cylinder of a pre-chamber
ignition engine. The cylinder may have a cylinder configuration
including an active pre-chamber that includes a fuel injector, a
spark plug, and an air and/or O.sub.2 injector, such as shown in
FIG. 1. The pre-chamber may be operated to provide an ignition
source to the cylinder according to the method of FIG. 2. However,
exhaust gases and injected air from the pre-chamber may enter the
cylinder, which may change the air-fuel ratio (AFR) of the
cylinder. Therefore, a controller of the engine may adjust cylinder
fueling based on amounts of pre-chamber exhaust gas and air
entering the cylinder during the compression stroke of the cylinder
according to the example method of FIG. 3. FIG. 4 shows an example
graph of a characteristic relationship between pressure in the
cylinder and a piston position within the cylinder, which may be
used by the controller to determine pre-chamber injection pressures
as well as to estimate gas flow from the pre-chamber to the
cylinder. Further, FIG. 5 shows an example timing diagram operating
a pre-chamber to purge gases to a cylinder, and FIG. 6 shows an
example timeline for operating a cylinder with cylinder fueling
compensation based on amounts of pre-chamber gases.
[0016] Turning now to the figures, FIG. 1 shows a partial view of a
single cylinder 130 of an internal combustion engine 10 that may be
included in a vehicle 5. Internal combustion engine 10 may be a
multi-cylinder engine. Cylinder (e.g., combustion chamber) 130
includes a coolant sleeve 114 and cylinder walls 132, with a piston
136 positioned therein and connected to a crankshaft 140.
Combustion chamber 130 is shown communicating with an intake
manifold 44 via an intake valve 4 and an intake port 22 and with an
exhaust manifold 48 via an exhaust valve 8 and an exhaust port 86.
A throttle 62 including a throttle plate 64 may be provided in an
intake passage upstream of intake manifold 44 for varying a flow
rate and/or pressure of intake air provided to the engine
cylinders.
[0017] An exhaust passage 135 can receive exhaust gases from other
cylinders of engine 10 in addition to cylinder 130. An exhaust gas
sensor 128 is shown coupled to exhaust passage 135 upstream of an
emission control device 178. Exhaust gas sensor 128 may be selected
from among various suitable sensors for providing an indication of
an exhaust gas air-fuel ratio (AFR), such as a linear oxygen sensor
or UEGO (universal or wide-range exhaust gas oxygen), a two-state
oxygen sensor or EGO (as depicted), a HEGO (heated EGO), a NOx
sensor, a HC sensor, or a CO sensor, for example. Emission control
device 178 may be a three-way catalyst, a NOx trap, various other
emission control devices, or combinations thereof.
[0018] External exhaust gas recirculation (EGR) may be provided to
the engine via a high pressure EGR system 83, delivering exhaust
gas from a zone of higher pressure in exhaust passage 135 to a zone
of lower pressure in intake manifold 44, downstream of throttle 62,
via an EGR passage 81. An amount EGR provided to intake manifold 44
may be varied by controller 12 via an EGR valve 80. For example,
controller 12 may be configured to actuate and adjust a position of
EGR valve 80 to adjust the amount of exhaust gas flowing through
EGR passage 81. EGR valve 80 may be adjusted between a fully closed
position, in which exhaust gas flow through EGR passage 81 is
blocked, and a fully open position, in which exhaust gas flow
through the EGR passage is enabled. As an example, EGR valve 80 may
be continuously variable between the fully closed position and the
fully open position. As such, the controller may increase a degree
of opening of EGR valve 80 to increase an amount of EGR provided to
intake manifold 44 and decrease the degree of opening of EGR valve
80 to decrease the amount of EGR provided to intake manifold 44. As
an example, EGR valve 80 may be an electronically activated
solenoid valve. In other examples, EGR valve 80 may be positioned
by an incorporated stepper motor, which may be actuated by
controller 12 to adjust the position of EGR valve 80 through a
range of discreet steps (e.g., 52 steps), or EGR valve 80 may be
another type of flow control valve. Further, EGR may be cooled via
passing through EGR cooler 85 within EGR passage 81. EGR cooler 85
may reject heat from the EGR gases to engine coolant, for
example.
[0019] Under some conditions, the EGR system may be used to
regulate a temperature of the air and fuel mixture within the
combustion chamber. Further, EGR may be desired to attain a desired
engine dilution, thereby increasing fuel efficiency and emissions
quality, such as emissions of nitrogen oxides. As an example, EGR
may be requested at low-to-mid engine loads. Thus, it may be
desirable to measure or estimate the EGR mass flow. EGR sensors may
be arranged within EGR passage 81 and may provide an indication of
one or more of mass flow, pressure, and temperature of the exhaust
gas, for example. Additionally, EGR may be desired after emission
control device 178 has attained its light-off temperature. An
amount of EGR requested may be based on engine operating
conditions, including engine load (as estimated via pedal position
sensor 134), engine speed (as estimated via a crankshaft
acceleration sensor), engine temperature (as estimated via an
engine coolant temperature sensor), etc. For example, controller 12
may refer to a look-up table having the engine speed and load as
the input and output a desired amount of EGR corresponding to the
input engine speed-load. In another example, controller 12 may
determine the desired amount of EGR (e.g., desired EGR flow rate)
through logic rules that directly take into account parameters such
as engine load, engine speed, engine temperature, etc. In still
other examples, controller 12 may rely on a model that correlates a
change in engine load with a change in a dilution requirement, and
further correlates the change in the dilution requirement with a
change in the amount of EGR requested. For example, as the engine
load increases from a low load to a mid load, the amount of EGR
requested may increase, and then as the engine load increases from
a mid load to a high load, the amount of EGR requested may
decrease. Controller 12 may further determine the amount of EGR
requested by taking into account a best fuel economy mapping for a
desired dilution rate. After determining the amount of EGR
requested, controller 12 may refer to a look-up table having the
requested amount of EGR as the input and a signal corresponding to
a degree of opening to apply to the EGR valve (e.g., as sent to the
stepper motor or other valve actuation device) as the output.
[0020] In the depicted view, intake valve 4 and exhaust valve 8 are
located at an upper region of combustion chamber 130. Intake valve
4 and exhaust valve 8 may be controlled by a controller 12 using
respective cam actuation systems including one or more cams. The
cam actuation systems may utilize one or more of variable
displacement engine (VDE), cam profile switching (CPS), variable
cam timing (VCT), variable valve timing (VVT), and/or variable
valve lift (VVL) systems to vary valve operation. In the depicted
example, intake valve 4 is controlled by an intake cam 151, and
exhaust valve 8 is controlled by an exhaust cam 153. The intake cam
151 may be actuated via an intake valve timing actuator 101 and the
exhaust cam 153 may be actuated via an exhaust valve timing
actuator 103 according to set intake and exhaust valve timings,
respectively. In some examples, the intake valves and exhaust
valves may be deactivated via the intake valve timing actuator 101
and exhaust valve timing actuator 103, respectively. The position
of intake cam 151 and exhaust cam 153 may be determined by camshaft
position sensors 155 and 157, respectively.
[0021] In some examples, the intake and/or exhaust valve may be
controlled by electric valve actuation. For example, cylinder 130
may alternatively include an intake valve controlled via electric
valve actuation and an exhaust valve controlled via cam actuation,
including CPS and/or VCT systems. In still other examples, the
intake and exhaust valves may be controlled by a common valve
actuator or actuation system or a variable valve timing actuator or
actuation system. The various valve control systems may be used to
vary a timing, open duration, and lift of intake valve 4 and
exhaust valve 8.
[0022] Cylinder 130 can have a compression ratio, which is a ratio
of volumes when piston 136 is at bottom dead center to top dead
center. Conventionally, the compression ratio is in a range of 9:1
to 10:1. However, in some examples where different fuels are used,
the compression ratio may be increased. This may happen, for
example, when higher octane fuels or fuels with higher latent
enthalpy of vaporization are used. The compression ratio may also
be increased if direct injection is used due to its effect on
engine knock.
[0023] As a non-limiting example, cylinder 130 is shown including a
cylinder fuel injector 66. Fuel injector 66 is shown coupled
directly to combustion chamber 130 for injecting fuel directly
therein in proportion to a pulse-width of a signal FPW1 received
from controller 12 via an electronic driver 168. In this manner,
fuel injector 66 provides what is known as direct injection
(hereafter also referred to as "DI") of fuel into cylinder 130. In
another example, injector 66 may be a port injector providing fuel
into the intake port upstream of cylinder 130. Further, while FIG.
1 shows fuel injected to the cylinder via a single injector, the
engine may alternatively be operated by injecting fuel via multiple
injectors, such as one direct injector and one port injector. For
example, both port and direct injectors may be included in a
configuration that is known as port fuel and direct injection
(PFDI). In such a configuration, controller 12 may vary a relative
amount of injection from each injector.
[0024] Fuel may be delivered to fuel injector 66 from a high
pressure fuel system 180 including one or more fuel tanks, fuel
pumps, and a fuel rail. Alternatively, fuel may be delivered by a
single stage fuel pump at a lower pressure. Further, while not
shown, the fuel tanks may include a pressure transducer providing a
signal to controller 12. Fuel tanks in fuel system 180 may hold
fuel with different fuel qualities, such as different fuel
compositions. These differences may include different alcohol
content, different octane, different heats of vaporization,
different fuel blends, and/or combinations thereof, etc. One
example of fuels with different heats of vaporization includes
gasoline as a first fuel type with a lower heat of vaporization and
ethanol as a second fuel type with a greater heat of vaporization.
In another example, the engine may use gasoline as a first fuel
type and an alcohol-containing fuel blend, such as E85 (which is
approximately 85% ethanol and 15% gasoline) or M85 (which is
approximately 85% methanol and 15% gasoline), as a second fuel
type. Other feasible substances include water, methanol, a mixture
of ethanol and water, a mixture of water and methanol, a mixture of
alcohols, etc. In this way, air and fuel are delivered to cylinder
130, which may produce a combustible air-fuel mixture.
[0025] Fuel may be delivered by fuel injector 66 to cylinder 130
during a single cycle of the cylinder. Further, the distribution
and/or relative amount of fuel delivered from cylinder fuel
injector 66 may vary with operating conditions. Furthermore, for a
single combustion event, multiple injections of the delivered fuel
may be performed per cycle. The multiple injections may be
performed during the compression stroke, intake stroke, or any
appropriate combination thereof.
[0026] In the example shown in FIG. 1, each cylinder 130 of engine
10 includes a pre-chamber 138 for initiating combustion.
Pre-chamber 138 is defined by pre-chamber walls 139 and includes a
spark plug 92, an air injector 94, and a pre-chamber fuel injector
96. Air injector 94 is shown directly coupled to pre-chamber 138
for injecting air and/or oxygen into the pre-chamber. In some
examples, air injector 94 is an electromagnetic (e.g., solenoid)
injector. One or more of ambient air, oxygen, and another
combustible gas may be delivered to air injector 94 from a
pre-chamber air source 190. In some examples, air injector 94 is an
electromagnetic (e.g., solenoid) injector, and may inject air
and/or O.sub.2 in proportion to a pulse-width of a signal APW
received from controller 12 via pre-chamber air source 190. Note
that in relation to pre-chamber air source 190, the term "air" may
refer herein to ambient air, oxygen (e.g., O.sub.2), hydrogen
(e.g., H.sub.2), or a mixture of such gases. In some examples, the
pre-chamber air source 190 supplies air injector 94 with ambient
air from an air intake passage of the engine, which may be stored
in a pressurized tank before injection. In other examples,
pre-chamber air source 190 supplies air injector 94 with
onboard-generated O.sub.2, which may be stored in a pressurized
tank before injection. For example, the pressurized tank of
pre-chamber air source 190 may be maintained at a desired pressure
by an associated pump. A pressure differential between the
pressurized tank and the pre-chamber and an open time of air
injector 94 (e.g., as determined by the pulse-width of the signal
APW) may determine the mass of air or O.sub.2 delivered to
pre-chamber 138, for example.
[0027] Pre-chamber fuel injector 96 is shown coupled directly to
pre-chamber 138 for injecting fuel directly therein in proportion
to a pulse-width of a signal FPW2 received from controller 12 via
an electronic driver 172. Fuel may be provided to pre-chamber fuel
injector 96 by high-pressure fuel system 180, described above.
Alternatively, fuel may be provided to pre-chamber fuel injector 96
from a dedicated pre-chamber fuel system that may be included
within or distinct from high-pressure fuel system 180. Thus, both
air and fuel are delivered to pre-chamber 138, which may produce an
air-fuel mixture with an air-fuel ratio (AFR) that may differ from
an AFR in cylinder 130. In one example, the AFR in pre-chamber 138
may be richer (e.g., have a higher proportion of fuel) than the AFR
in cylinder 130. In another example, the AFR in the pre-chamber may
be the same as the AFR in the cylinder. In yet another example, the
AFR in pre-chamber 138 may be leaner (e.g., have a higher
proportion of air) than the AFR in cylinder 130.
[0028] Further, the pre-chamber walls 139 may include a plurality
of openings, such as an opening 142 shown in FIG. 1. Opening 142
provides an orifice between pre-chamber 138 and cylinder 130,
fluidically coupling an interior of pre-chamber 138 to an interior
of cylinder 130. As such, during some conditions, gases may flow
between the interior of pre-chamber 138 and the interior of
cylinder 130. For example, gases (e.g., air, fuel, and/or residual
combustion gases) may flow through opening 142 with a
directionality and rate based on a pressure difference across
opening 142 (e.g., between the interior of pre-chamber 138 and the
interior of cylinder 130). Opening 142 (along with any other
openings in pre-chamber walls 139) may also provide an ignition
flame from pre-chamber 138 to cylinder 130, as will be elaborated
below.
[0029] An ignition system 88 may provide an ignition spark to
pre-chamber 138 via spark plug 92 in response to a spark advance
signal SA from controller 12, under select operating modes. A
timing of signal SA may be adjusted based on engine operating
conditions and a driver torque demand. For example, spark may be
provided at maximum brake torque (MBT) timing to maximize engine
power and efficiency. Controller 12 may input engine operating
conditions, including engine speed, engine load, and exhaust gas
AFR, into a look-up table, which may output the corresponding MBT
timing for the input engine operating conditions. In other
examples, spark may be retarded from MBT to prevent an occurrence
of knock. In still other examples, spark may be retarded from MBT
to reduce engine torque, such as due to a decrease in
driver-demanded torque or a transmission gear shift event. When
spark plug 92 provides the ignition spark to pre-chamber 138, the
air-fuel mixture within the pre-chamber may combust, the increased
pressure of combustion sending jets of flame into cylinder 130 via
the plurality of openings in the pre-chamber walls 139, including
opening 142. The plurality of openings may be arranged such that
the jets of flame are evenly distributed in cylinder 130. The jets
of flame may ignite the air-fuel mixture in cylinder 130, causing
combustion. After combustion, a mixture of exhaust gases from both
pre-chamber 138 and cylinder 130 may be exhausted from cylinder 130
to exhaust manifold 48 via opening of exhaust valve 8.
[0030] Engine 10 may be controlled at least partially by controller
12 and by input from a vehicle operator 113 via an accelerator
pedal 116 and an accelerator pedal position sensor 118 and via a
brake pedal 117 and a brake pedal position sensor 119. The
accelerator pedal position sensor 118 may send a pedal position
signal (PP) to controller 12 corresponding to a position of
accelerator pedal 116, and the brake pedal position sensor 119 may
send a brake pedal position (BPP) signal to controller 12
corresponding to a position of brake pedal 117. Controller 12 is
shown in FIG. 1 as a microcomputer, including a microprocessor unit
102, input/output ports 104, an electronic storage medium for
executable programs and calibration values shown as a read-only
memory 106 in this particular example, random access memory 108,
keep alive memory 110, and a data bus. Storage medium read-only
memory 106 can be programmed with computer readable data
representing instructions executable by microprocessor 102 for
performing the methods and routines described herein as well as
other variants that are anticipated but not specifically
listed.
[0031] Controller 12 may receive various signals from sensors
coupled to engine 10, in addition to those signals previously
discussed, including a measurement of inducted mass air flow (MAF)
from a mass air flow sensor 123, an engine coolant temperature
signal (ECT) from a temperature sensor 112 coupled to coolant
sleeve 114, signal EGO from exhaust gas sensor 128, which may be
used by controller 12 to determine the AFR of the exhaust gas, an
exhaust gas temperature signal (EGT) from a temperature sensor 158
coupled to exhaust passage 135, a profile ignition pickup signal
(PIP) from a Hall effect sensor 120 (or other type) coupled to
crankshaft 140, a throttle position (TP) from a throttle position
sensor coupled to throttle 62, and an absolute manifold pressure
signal (MAP) from a MAP sensor 122 coupled to intake manifold 44.
An engine speed signal, RPM, may be generated by controller 12 from
signal PIP. The manifold pressure signal MAP from the manifold
pressure sensor may be used to provide an indication of vacuum or
pressure in the intake manifold.
[0032] Based on input from one or more of the above-mentioned
sensors, controller 12 may adjust one or more actuators, such as
cylinder fuel injector 66, throttle 62, spark plug 92, pre-chamber
fuel injector 96, pre-chamber air injector 94, the intake/exhaust
valves and cams, etc. The controller may receive input data from
the various sensors, process the input data, and trigger the
actuators in response to the processed input data based on
instruction or code programmed therein corresponding to one or more
routines, examples of which is described with respect to FIGS. 2
and 3.
[0033] In some examples, vehicle 5 may be a hybrid vehicle with
multiple sources of torque available to one or more vehicle wheels
160. In other examples, vehicle 5 is a conventional vehicle with
only an engine. In the example shown in FIG. 1, the vehicle
includes engine 10 and an electric machine 161. Electric machine
161 may be a motor or a motor/generator and thus may also be
referred to herein as an electric motor. Electric machine 161
receives electrical power from a traction battery 170 to provide
torque to vehicle wheels 160. Electric machine 161 may also be
operated as a generator to provide electrical power to charge
battery 170, for example, during a braking operation.
[0034] Crankshaft 140 of engine 10 and electric machine 161 are
connected via a transmission 167 to vehicle wheels 160 when one or
more clutches 166 are engaged. In the depicted example, a first
clutch 166 is provided between crankshaft 140 and electric machine
161, and a second clutch 166 is provided between electric machine
161 and transmission 167. Controller 12 may send a signal to an
actuator of each clutch 166 to engage or disengage the clutch, so
as to connect or disconnect crankshaft 140 from electric machine
161 and the components connected thereto, and/or connect or
disconnect electric machine 161 from transmission 167 and the
components connected thereto. Transmission 167 may be a gearbox, a
planetary gear system, or another type of transmission. The
powertrain may be configured in various manners including as a
parallel, a series, or a series-parallel hybrid vehicle.
[0035] As described above, FIG. 1 shows only one cylinder of a
multi-cylinder engine. As such, each cylinder may similarly include
its own set of intake/exhaust valves, fuel injector(s), spark plug,
etc. It will be appreciated that engine 10 may include any suitable
number of cylinders, including 2, 3, 4, 5, 6, 8, 10, 12, or more
cylinders. Further, each of these cylinders can include some or all
of the various components described and depicted by FIG. 1 with
reference to cylinder 130.
[0036] Next, FIG. 2 shows an example method for operating a
pre-chamber of an engine to combust an air-fuel mixture within the
pre-chamber. As one example, operating the pre-chamber provides an
ignition source for a cylinder of the engine. As another example,
operating the pre-chamber increases a temperature of the
pre-chamber. Method 200 will be described with respect to engine 10
and the cylinder configuration shown in FIG. 1, although method 200
may be applied in other systems that include a pre-chamber with a
spark plug, a fuel injector, and an air/O.sub.2 injector. Further,
method 200 will be described for one pre-chamber and cylinder pair,
although it may be understood that method 200 may be simultaneously
and/or sequentially executed for every cylinder of the engine.
Instructions for carrying out method 200 and the rest of the
methods included herein may be executed by a controller, such as
controller 12 of FIG. 1, based on instructions stored on a memory
of the controller and in conjunction with signals received from
sensors of the engine system, such as the sensors described above
with reference to FIG. 1. The controller may employ actuators of
the pre-chamber ignition system, including a pre-chamber fuel
injector (e.g., pre-chamber fuel injector 96 of FIG. 1), a
pre-chamber spark plug (e.g., pre-chamber spark plug 92 of FIG. 1),
and a pre-chamber air injector (e.g., pre-chamber air injector 94
shown in FIG. 1) to adjust engine operation according to the
methods described below.
[0037] At 202, method 200 includes estimating and/or measuring
operating conditions. The operating conditions may include, for
example, vehicle speed, engine speed, engine load, an engine
temperature, an exhaust gas AFR, an accelerator pedal position, a
brake pedal position, and a position of a throttle (e.g., throttle
position). The operating conditions may be measured by one or more
sensors communicatively coupled to the controller or may be
inferred based on available data. For example, the accelerator
pedal position may be measured by an acceleration position sensor,
such as acceleration pedal position sensor 118 of FIG. 1, and the
brake pedal position may be measured by a brake pedal position
sensor, such as brake pedal position sensor 119 of FIG. 1.
Together, the accelerator pedal position and the brake pedal
position may indicate a demanded amount of engine torque. As
another example, the AFR may be determined based on an oxygen level
detected by an exhaust gas oxygen sensor, such as exhaust gas
sensor 128 of FIG. 1. Similarly, the throttle position may be
measured using a throttle position sensor coupled to the
throttle.
[0038] At 204, method 200 includes determining whether a firing
event is requested in the pre-chamber. In some examples, the
pre-chamber firing event may be requested during nominal engine
operation to provide an ignition source for the cylinder during
each combustion cycle. A combustion cycle (e.g., a cylinder cycle)
may refer to a four stroke movement of a piston of the cylinder,
the four strokes including an intake stroke, a compression stroke,
a power stroke, and an exhaust stroke. In alternative examples, the
combustion cycle may refer to a two stroke movement of the piston.
When the pre-chamber firing event is requested to provide an
ignition source for the cylinder during a combustion cycle, the
firing event may occur during the end of a compression stroke. In
another example, the pre-chamber firing event may be requested
during an exhaust stroke of a combustion cycle to increase a
temperature of the pre-chamber.
[0039] If the pre-chamber firing event is not requested at 204,
method 200 proceeds to 206, and includes not operating the
pre-chamber. In some examples, the pre-chamber firing event may not
be requested while engine combustion is discontinued. For example,
engine combustion may be discontinued while the engine is shut down
or during a fuel-cut condition, such as when cylinder fueling is
shut off while the vehicle speed decreases. In another example, the
pre-chamber firing event may not be requested when the pre-chamber
firing event has already been performed during the combustion
cycle. Not operating the pre-chamber may include not injecting fuel
and air into the pre-chamber so that there is no air-fuel mixture
for combustion within the pre-chamber. Without an air-fuel mixture
to combust, not operating the pre-chamber may further include not
activating the spark plug in the pre-chamber. Further, because
combustion is not performed in the pre-chamber, not operating the
pre-chamber may further include not providing an ignition source to
the cylinder. However, in other examples, an alternative ignition
source may be provided to the cylinder (e.g., via a cylinder spark
plug that is independent from the pre-chamber spark plug or via
compression ignition). In one example, the controller may adjust
the pulse-widths of actuation signals to the fuel injector and the
air injector such that no air-fuel mixture is injected into the
pre-chamber. For example, no actuation signal may be sent to each
of the fuel injector and the air injector. Further, the controller
may adjust a control signal to the ignition system of the engine
such that the spark plug in the pre-chamber is not activated.
[0040] If a pre-chamber firing event is requested at 204, method
200 proceeds to 208 and includes determining a desired pre-chamber
AFR (e.g., a ratio of an amount of air injected to an amount of
fuel injected into the pre-chamber). The desired AFR of the
pre-chamber may be determined by the controller based on the AFR of
the cylinder, such that combustion of an air-fuel mixture in the
pre-chamber ignites an air-fuel mixture in the cylinder while
minimizing emissions, as an example. For example, the controller
may input the AFR of the cylinder and the current engine operating
conditions, such as engine temperature and fuel composition, into
one or more look-up tables, function, and maps, which may output
the desired pre-chamber AFR to achieve combustion. As an example,
the desired AFR of the pre-chamber may be stoichiometry. As another
example, the desired AFR of the pre-chamber may be rich relative to
stoichiometry during an engine cold start condition, which may
increase combustion stability in the cold start condition, for
example. As still another example, the desired AFR of the
pre-chamber may be richer than stoichiometry when fuels with higher
evaporation temperatures, such as E85, are used in order to account
for evaporated fuel that participates in the combustion and
non-evaporated fuel that does not participate in combustion to
achieve a substantially stoichiometry combustion with the
evaporated fuel. As yet another example, the desired AFR of the
pre-chamber may be adjusted from stoichiometry when an operating
AFR of the cylinder is adjusted from stoichiometry such that when
the combustion gases from the cylinder and the pre-chamber are
combined, the combined gases have an AFR approximately equal to
stoichiometry.
[0041] At 210, method 200 includes determining a desired
pre-chamber spark timing for the pre-chamber firing event.
Determining the desired pre-chamber spark timing may include
determining when to ignite the air-fuel mixture in the pre-chamber
relative to a position of a piston of the cylinder. Although a
cylinder spark plug firing induces combustion in a cylinder of a
traditional spark-ignition engine, in an engine with pre-chamber
ignition, combustion in the pre-chamber induces combustion in the
cylinder. Thus, just as cylinder spark timing in the traditional
spark-ignition engine may be adjusted relative to the spark timing
for maximum brake torque (MBT) based on engine operating
conditions, the timing of the pre-chamber firing event may be
shifted relative to MBT based on engine operating conditions in
order to achieve a desired cylinder ignition timing. For example,
the pre-chamber spark timing may be retarded relative to MBT timing
to increase an exhaust gas temperature, while the pre-chamber spark
timing may be advanced closer to MBT timing to increase a torque
output of the cylinder. As another example, if the engine is
borderline limited and is unable to operate at MBT timing, engine
knock control may advance or retard the pre-chamber spark timing to
operate the engine at the borderline limit. In one example, the
controller may input one or more engine operating conditions (e.g.,
engine speed, engine load, the exhaust gas temperature, a
borderline knock limit, and cylinder AFR) into one or more look-up
tables, functions, or maps to determine the desired timing for the
pre-chamber firing event. In another example, the controller may
make a logical determination (e.g., regarding the pre-chamber spark
timing) based on logic rules that are a function of the one or more
engine operating conditions.
[0042] At 212, method 200 includes injecting air into the
pre-chamber. In some examples, the air injected may be ambient air
from an intake manifold of the engine, while in other examples, the
pre-chamber air injector may provide onboard-generated O.sub.2 or
another combustible gas such as H.sub.2. As one example, a single
air injection event may not only provide air for combustion, but
may also purge residual gases from a previous pre-chamber firing
event from the pre-chamber. In another example, a single air
injection may provide air for combustion without purging a
significant amount of residual gas from the pre-chamber. As another
example, a first air injection event may purge residual gases from
the previous pre-chamber firing event from the pre-chamber, and a
second air injection event may provide air for combustion in the
pre-chamber. In yet another example, a third air injection may
provide additional air for combustion in the pre-chamber, or may
provide an alternative combustible gas (e.g., H.sub.2) to the
pre-chamber. For each of one or more injection events, the
controller may adjust an amount of air injected into the
pre-chamber based on the desired AFR of the pre-chamber, as
determined at 208, and the position of the piston in the cylinder.
For example, the controller may input the engine operating
conditions, including the piston position and the desired AFR of
the pre-chamber, into a look-up table, algorithm, or map, which may
output a desired air injection amount. In some examples, the air
injection amount may be held substantially constant while only the
fuel injection amount is varied to compensate for changes in the
desired AFR. For example, an amount of air injected may be
approximately equal to a volume in the pre-chamber.
[0043] After determining the amount of air to be injected, the
controller may inject the desired air amount by adjusting the
pulse-width of an actuation signal sent to the pre-chamber air
injector. Further, an injection pressure may be above a peak
pressure in the cylinder. Because of this, some of the air injected
may flow into the cylinder (e.g., due to the pressure in the
cylinder being lower than the pressure in the pre-chamber). An
amount of air injected to the pre-chamber that flows into the
cylinder may be determined based on a pressure difference between
the air injector pressure and the pressure in the cylinder and a
size of opening(s) in the pre-chamber walls. This value may be used
in adjusting cylinder fuel control, as will be elaborated with
respect to FIG. 3.
[0044] At 214, method 200 includes injecting fuel into the
pre-chamber. The controller may adjust an amount of fuel injected
into the pre-chamber based on the desired AFR of the pre-chamber,
as determined at 208, and the amount of air injected at 212. For
example, the controller may input the desired pre-chamber AFR into
one or more look-up tables, functions, and maps, which may output a
desired fuel amount to inject that will achieve the desired AFR in
the pre-chamber. In one example, the controller may inject the
desired fuel amount by adjusting the pulse-width of an actuation
signal sent to the pre-chamber fuel injector, such as FPW2 shown in
FIG. 1. The injected fuel may mix with the injected air (e.g.,
injected at 212) to form an air-fuel mixture.
[0045] At 216, method 200 includes actuating the pre-chamber spark
plug to generate a spark in the pre-chamber. The controller may
generate a control signal (e.g., signal SA) that is sent an
ignition system (e.g., ignition system 88 of FIG. 1) to actuate the
pre-chamber spark plug at the pre-chamber spark timing determined
at 210. Generating the spark in the pre-chamber may cause the
air-fuel mixture in the pre-chamber to combust, sending jets of hot
gas and flame into the cylinder via a plurality of holes in the
pre-chamber walls. When the cylinder also includes a combustible
air-fuel mixture, the jets of hot gas and flame ignite the air-fuel
mixture in the cylinder. After 216, method 200 may end.
[0046] In this way, the pre-chamber of a cylinder may be operated
to ignite a first air-fuel mixture within the pre-chamber, which
may further ignite a second air-fuel mixture in the cylinder. In
some examples, method 200 may run continuously during nominal
engine operation in order to continuously provide a cylinder
ignition source when indicated. With active air and fuel injection
in the pre-chamber, the AFR of the first air-fuel mixture may be
predicted based on injection amounts of the air and fuel, which may
increase ignition control, and active air injection may further
purge the pre-chamber of residual gases from previous combustion
cycles, for example. Further, with jets of flame and hot gas as the
cylinder ignition source, the second air-fuel mixture in the
cylinder may combust more fully and with a lower peak combustion
temperature than in an engine with a spark plug as the cylinder
ignition source. Thus, in a pre-chamber ignition system, the second
air-fuel mixture in the cylinder may be commanded lean relative to
stoichiometry without a reduction in combustion stability and
without an increase in NO.sub.x emissions and/or combustion
temperatures. Further, active air injection may further purge the
pre-chamber of residual gases from previous cylinder cycles, for
example. Accordingly, actively injecting both air and fuel into the
pre-chamber increases a control and an accuracy of the AFR of the
first air-fuel mixture compared with passive pre-chamber systems
(e.g., pre-chamber systems without active air injection and/or
active fuel injection). As a result, the pre-chamber may reliably
operate over a wider range of engine operating conditions to
provide cylinder ignition.
[0047] However, in active pre-chamber ignition systems, such as the
cylinder configuration shown in FIG. 1, pre-chamber gases may enter
the corresponding cylinder prior to cylinder combustion, which may
change the AFR of the second air-fuel mixture (e.g., the AFR in the
cylinder). Pre-chamber gases may include air injected into the
pre-chamber and residual gases (e.g., exhaust gases from a previous
combustion cycle) purged from the pre-chamber. For example, a
fraction of air injected into the pre-chamber may flow into the
corresponding cylinder before cylinder combustion. As another
example, the pre-chamber residual gases may flow into the cylinder
before cylinder combustion. The addition of such pre-chamber gases
to the cylinder may cause the cylinder to operate at a different
AFR than the commanded AFR. For example, if pre-chamber air (e.g.,
air injected into the pre-chamber) enters the cylinder before
cylinder combustion, the cylinder AFR may be leaner (e.g., have a
higher ratio of air to fuel) than commanded. As another example, if
fuel-rich residual gases are purged into the cylinder prior to
cylinder combustion, the overall cylinder AFR may be richer (e.g.,
have a lower ratio of air to fuel) than commanded. Such AFR
deviations (e.g., uncommanded lean operation and/or uncommanded
rich operation) may increase vehicle emissions, for example.
Methods for determining cylinder fueling that compensate for the
addition of pre-chamber gases to the cylinder are desired in order
to reduce fueling errors in the cylinder.
[0048] Thus, FIG. 3 shows an example method for adjusting cylinder
fueling based on amounts of pre-chamber gases in a cylinder before
pre-chamber combustion (e.g., cylinder fuel compensation). As
illustrated in FIG. 1, the cylinder may include a cylinder fuel
injector (e.g., cylinder fuel injector 66), which may inject fuel
into the cylinder, and a pre-chamber located in a clearance volume
of the cylinder. The pre-chamber and may include a pre-chamber fuel
injector (e.g., fuel injector 96 of FIG. 1), an air injector (e.g.,
air injector 94 of FIG. 1), and a spark plug (e.g., spark plug 92
of FIG. 1). As such, method 300 will be described with respect to
the cylinder configuration shown in FIG. 1, although method 300 may
be applied in other systems that include pre-chamber ignition.
Instructions for carrying out method 300 may be executed by a
controller, such as controller 12 of FIG. 1, based on instructions
stored on a memory of the controller and in conjunction with signal
received from sensors of the engine system, such as the sensors
described above with reference to FIG. 1. The controller may employ
engine actuators of the engine system to adjust cylinder fueling
according to the method described below. Method 300 will be
described with respect to a single cylinder including a
pre-chamber, although method 300 may be performed simultaneously
for a plurality of cylinders in a multi-cylinder engine with
pre-chamber ignition.
[0049] At 302, method 300 includes estimating and/or measuring
operating conditions. The operating conditions may include, for
example, vehicle speed, engine speed, engine load, an exhaust gas
AFR, absolute manifold pressure, mass air flow, and throttle
position. The operating conditions may be measured by one or more
sensors communicatively coupled to the controller or may be
inferred based on available data. For example, the exhaust gas AFR
may be determined based on a measurement from an exhaust gas oxygen
sensor, such as exhaust gas oxygen sensor 128 of FIG. 1. As another
example, the absolute manifold pressure may be measured by an
absolute manifold pressure sensor, such as MAP sensor 122 of FIG.
1. As yet another example, the mass air flow may be measured by a
mass air flow (MAF) sensor, such as MAF sensor 123 shown in FIG. 1.
As another example, the controller may use output from a throttle
position (TP) sensor to determine a position of the throttle.
[0050] At 304, method 300 includes estimating cylinder pressure,
which includes a peak cylinder pressure. For example, the
controller may estimate and/or determine a characteristic
relationship between a cylinder pressure and a piston position.
Turning briefly to FIG. 4, an example plot 400 of a characteristic
relationship between a cylinder pressure and a piston position of
the cylinder during a compression stroke and a power stroke of the
cylinder is shown. For plot 400, the vertical axis shows cylinder
pressure relative to an absolute manifold pressure. The horizontal
axis shows piston position relative to top dead center (TDC) and
bottom dead center (BDC) during the compression stroke and the
power stroke of the cylinder.
[0051] Plot 400 includes a non-linear curve 402 that illustrates
the relationship between the cylinder pressure and the piston
position. A controller, such as controller 12 of FIG. 1, may
estimate the cylinder pressure, including a peak cylinder pressure,
based on the Ideal Gas Law, for example, which states a
relationship between volume, pressure, and temperature for a closed
container of a gas. Specifically, the Ideal Gas Law states that a
pressure of the gas and a volume of the gas are inversely related.
For example, when the piston position is at BDC, the cylinder
volume is high, and so the relative cylinder pressure is low. As
another example, when the piston position is at TDC (shown by a
dashed line 416), the cylinder volume is low, and so the cylinder
pressure is higher. Further, a peak cylinder pressure (e.g.,
P.sub.p) may be achieved when the cylinder volume is the lowest at
TDC. As used herein, the peak cylinder pressure is defined as the
maximum air pressure in the cylinder based on cylinder volume and
is shown by a dashed line 404. Although the cylinder pressure may
further increase during combustion, combustion pressures are not
represented by curve 402. Further, the peak cylinder pressure may
vary according to engine operating conditions. As an example, the
peak cylinder pressure may be lower in low load operating
conditions relative to the peak cylinder pressure in high load
operating conditions. That is, when the engine is operating with a
more open throttle, more air enters the engine, resulting in a
higher peak cylinder pressure during the compression stroke before
ignition and combustion.
[0052] Returning to FIG. 3, thus, based on the characteristic
relationship between piston position and cylinder pressure, the
controller may estimate the pressure in the cylinder throughout a
combustion cycle. In particular, air charge, which may be
determined based on intake manifold pressure (e.g., MAP), will
determine a mass of air in the cylinder, and then a relationship
between the mass of air in the cylinder and a volume of the
cylinder (e.g., the Ideal Gas Law) may be used to determine the
cylinder pressure. For example, the volume of the cylinder
throughout a combustion cycle may be estimated based on piston
position, crank position, stroke, bore, and connecting rod length.
As one example, the controller may input the current operating
conditions, such as engine speed, engine temperature, and intake
manifold pressure, into one or more look-up tables, functions, or
maps, which may output the estimated cylinder pressure relative to
piston position. Further, the controller may estimate the peak
cylinder pressure by inputting the current engine operating
conditions, such as engine speed, engine temperature, and intake
manifold pressure, into one or more look-up tables, functions, or
maps. In some examples, the controller may actively calculate the
estimated cylinder pressure in real-time or at pre-determined
intervals, including the peak cylinder pressure, while in other
examples, the controller may access pre-determined estimations
stored in look-up tables and/or maps in controller memory according
to the engine operating conditions.
[0053] At 306, method 300 includes injecting air into the
pre-chamber during the compression stroke at a pressure greater
than or equal to the peak cylinder pressure during the compression
stroke. Further, the air may be injected one or more times at the
pressure higher than peak cylinder pressure for each injection
event. For example, a first air injection may be a purge injection
that pushes out pre-chamber exhaust gases, which may remain in the
pre-chamber from a previous combustion cycle, and a second air
injection may be provided for combustion. Returning to FIG. 4, the
controller may perform said air injections during the compression
stroke, with injection timing based on cylinder pressure. As a
non-limiting example, plot 400 includes a purging region 406
between a piston position 410 and a piston position 412. In purging
region 406, the controller may command air injection in the
pre-chamber while pressure in the cylinder is low at piston
position 410, which may encourage purging pre-chamber exhaust gases
into the cylinder. As another non-limiting example, plot 400
includes an injection region 408 between piston position 412 and a
piston position 414. In injection region 408, air may be injected
into the pre-chamber according to the method of FIG. 2 to introduce
air into the pre-chamber before pre-chamber combustion.
[0054] Returning to 306 of FIG. 3, the pressure of air injected
into the pre-chamber during each of the first air injection and the
second air injection may be determined by inputting engine
operating conditions (e.g., engine load and engine temperature) and
the peak cylinder pressure into one or more look-up tables, maps,
or functions. Further, the air is injected into the pre-chamber at
or above the peak cylinder pressure by actuating the air injector
during the compression stroke, for example. For example, for each
of the first air injection and the second air injection, the
controller may adjust a pulse width of an actuation signal sent to
the air injector in order to inject a determined amount of air
(e.g., ambient air, O.sub.2, or the like) into the pre-chamber at
the determined air pressure. Injecting the first air injection at
the pressure at or above peak cylinder pressure may promote purging
of pre-chamber exhaust gas into the cylinder, for example. As
another example, injecting the second air injection at or above
peak cylinder pressure may increase mixing of air and fuel in the
pre-chamber, which may increase ignitibility of a first air-fuel
mixture (e.g., the air-fuel mixture in the pre-chamber). However,
in some operating conditions, such as a fuel cut condition, a
single air injection may be performed in order to decrease an
amount of oxygen escaping the pre-chamber.
[0055] At 308, method 300 includes injecting fuel into the
pre-chamber at a pressure greater than or equal to the peak
cylinder pressure. Further, the pre-chamber fuel injection may be
performed during the injection region 408 of FIG. 4 introduced
above. Pre-chamber fuel injected at 308 may mix with pre-chamber
air injected at 306, during the second air injection, for example,
and may create the first air-fuel mixture. For example, a desired
amount of fuel is injected into the pre-chamber by actuating the
fuel injector during the compression stroke. The desired amount of
fuel may be determined according to the method of FIG. 2. The
pressure of fuel injected into the pre-chamber may be determined
based on engine operating conditions by referring to one or more
look-up tables, maps, or functions, and further may be calibrated
to promote combustion stability. For example, the controller may
adjust a pulse width of an actuation signal sent to the fuel
injector to inject the desired amount of fuel into the pre-chamber
at the determined fuel pressure. Injecting the fuel at or above
peak cylinder pressure may promote flow into the pre-chamber, for
example. As another example, injecting the fuel above peak cylinder
pressure may increase mixing of air and fuel in the pre-chamber,
which may increase ignitibility of the air-fuel mixture in the
pre-chamber. By injecting air into the pre-chamber at 306 and
injecting fuel into the pre-chamber at 308, the pre-chamber may be
filled with the first air-fuel mixture.
[0056] At 310, method 300 includes determining amounts of
pre-chamber gases in the cylinder. For example, after a pre-chamber
combustion, jets of flame and hot gas enter the cylinder via a
plurality of openings, but a portion of exhaust gas from the
pre-chamber combustion remains in the pre-chamber until being
purged into the cylinder via the purge injection described above at
306. Further, a portion of air injected via the purge injection may
enter the cylinder prior to combustion. Further still, an amount of
unburnt fuel may also escape the cylinder during the purge
injection. Therefore, a composition of the pre-chamber gases in the
cylinder may include a mixture of burnt exhaust gas from the
previous combustion cycle, purging air, and unburnt fuel from the
previous combustion cycle, and determining the amounts of the
pre-chamber gases in the cylinder may include determining an amount
of exhaust gas purged from the pre-chamber (or a proportion of the
exhaust gas in a total amount of pre-chamber gases), an amount of
air from the purge injection (or a proportion of air in the total
amount of pre-chamber gases), and an amount of unburnt fuel purged
from the pre-chamber (or a proportion of unburnt fuel in the total
amount of pre-chamber gases). The amount of pre-chamber exhaust gas
purged to the cylinder and the amount of pre-chamber air from the
purge injection may be determined at least partially based on the
pressure in the cylinder during the purge injection, for example.
As another example, the amount of pre-chamber exhaust gas purged to
the cylinder and the amount of pre-chamber air from the purge
injection in the cylinder may be determined based on a pressure
difference between the pre-chamber and the cylinder across the
plurality of openings, or orifices, of the pre-chamber. For
example, the controller may input the cylinder pressure during the
purge injection and the pressure of the purge injection into one or
more look-up tables, algorithms, or maps, which may output the
amount of pre-chamber exhaust gas and/or the amount of pre-chamber
air from the purge injection in the cylinder. As another example,
the controller may estimate cylinder pressure during the
pre-chamber air injection and may determine the amount of
pre-chamber air in the cylinder by inputting the estimated cylinder
pressure and pre-chamber injection amounts into one or more look-up
tables, maps, or functions. The amount of pre-chamber air in the
cylinder may be a fraction of the air injected into the pre-chamber
for purging (e.g., during the purging region 406 of FIG. 4).
[0057] As another example, the amount of exhaust gases purged from
the pre-chamber may be determined based on a volume of exhaust
gases purged from the pre-chamber (e.g., during the purging region
406 of FIG. 4), which may be equal to a volume of the pre-chamber
on the previous combustion cycle. Thus, in some examples, the
amount of exhaust gases purged from the pre-chamber may be
determined based on a known relationship between cylinder pressure,
a geometry of the pre-chamber, and a geometry of the pre-chamber
openings, by referring to one or more look-up tables, maps, or
functions. For example, the controller may estimate cylinder
pressure during pre-chamber exhaust gas purging and may determine
the amount of exhaust gas by inputting the estimated cylinder
pressure into one or more look-up tables, maps, or functions. As
another example, the amount of unburnt fuel from the pre-chamber in
the cylinder may be determined by inputting a fuel injection
pressure, a fuel injection amount, and a spark timing from the
previous combustion cycle into one or more look-up tables, maps, or
functions.
[0058] At 312, method 300 includes determining cylinder fueling
based on the amounts of pre-chamber gases in the cylinder.
Specifically, determining cylinder fueling may include determining
an amount of fuel for injection in the cylinder in order to operate
the cylinder a desired AFR. The desired AFR for the cylinder may be
stoichiometry, for example. In other examples, the desired AFR for
the cylinder may be lower (e.g., richer) or higher (e.g., leaner)
than stoichiometry. The controller may determine the amount of fuel
for injection in the cylinder based on the desired AFR, the amounts
of pre-chamber gases in the cylinder, and an amount of air inducted
into the cylinder during the intake stroke. For example, the amount
of fuel for injection in the cylinder may be equal to the air mass
inducted into the cylinder, added to the amount of air purged from
the pre-chamber, less the amount of exhaust gas purged from the
pre-chamber, less the amount of unburnt fuel purged from the
pre-chamber. In one example, when the controller determines that
additional purging air is in the cylinder, it may increase the
cylinder fueling amount in order to maintain stoichiometry in the
cylinder. In another example, when the controller determines that
additional fuel-rich residual gases are in the cylinder, it may
decrease the cylinder fueling amount in order to maintain
stoichiometry in the cylinder. Although air and fuel from the
second air-fuel mixture may escape into the pre-chamber during the
injection region 408 of FIG. 4, such leakage may be considered
stoichiometric, for example, and may not be compensated for in the
cylinder fuel adjustment. The controller may determine the amount
of air inducted during the intake stroke based on output from one
or more of the MAP sensor, the throttle position sensor, and the
MAF sensor, combined with an intake valve opening time, by
referring to one or more look-up tables, maps, or functions.
Further, in cylinder configurations with external EGR, such as the
cylinder configuration of FIG. 1, the controller may adjust the
determined cylinder fueling based on an amount of EGR flowing into
the cylinder and an AFR of the EGR by referring to one or more
look-up tables, graphs, or functions.
[0059] At 314, method 300 includes injecting fuel into the
cylinder. For example, fuel is injected into the cylinder by
actuating the cylinder fuel injector during the compression stroke.
For example, the controller may adjust a pulse width of an
actuation signal sent to the cylinder fuel injector to inject the
determined amount of fuel (e.g., as determined at 312) into the
cylinder during the compression stroke. In some examples, the
determined amount of fuel may be injected in a single injection
event, while in other examples, the determined amount of fuel may
be distributed over a plurality of injection events.
[0060] At 316, method 300 includes actuating the pre-chamber spark
plug to ignite the cylinder fuel. The spark ignites the first
air-fuel mixture inside the pre-chamber, causing a combustion
reaction that then ignites the second air-fuel mixture in the
cylinder. For example, the controller may actuate the spark plug
via a spark advance signal (e.g., signal SA shown in FIG. 1). In
some examples, the controller may further determine a spark timing
based on the relationship between cylinder pressure and piston
position by referring to one or more look-up tables, maps, or
functions. For example, the controller may actuate the pre-chamber
spark plug at a desired piston position for combustion in the
cylinder. As a non-limiting example, the pre-chamber spark plug may
be actuated at a piston position before TDC (shown by dashed line
416 in FIG. 4). Method 300 then ends. For example, method 300 may
be repeated during each combustion cycle to actively manage
cylinder fueling.
[0061] In this way, a cylinder with a pre-chamber ignition system
may be operated to provide torque to an engine by combusting an
air-fuel mixture, and cylinder fueling may be adjusted to
compensate for the pre-chamber gases. Further, the cylinder fueling
may be adjusted based on both an amount and composition of the
pre-chamber gases in the cylinder. For example, as an amount and/or
proportion of unburnt fuel from the pre-chamber gases increases,
the cylinder fueling may be further decreased. As another example,
as an amount and/or proportion of combustion gases from the
pre-chamber increases, the cylinder fueling may be further
increased. As still another example, as an amount and/or proportion
of air from the pre-chamber increases, the cylinder fueling may be
further increased. As a result, an accuracy of the cylinder fueling
may be increased and a desired AFR of the cylinder may be more
accurately achieved. By accurately controlling the AFR of the
cylinder, an efficiency of an emission control device may be
increased, thereby increasing vehicle emissions. Further, fuel
vehicle fuel efficiency may be increased by not inadvertently
operating the cylinder rich.
[0062] Turning now to FIG. 5, an exemplary timing chart 500 of
operating a cylinder with pre-chamber ignition, including
pre-chamber purging, is shown. The cylinder may be cylinder 130 of
engine 10 in FIG. 1, for example, and may include a pre-chamber
ignition system (e.g., pre-chamber 138 of FIG. 1). Timing chart 500
shows one combustion cycle, wherein the combustion cycle (e.g., a
cylinder cycle) refers to four strokes of an engine cycle within a
cylinder. A piston position relative to top dead center (TDC),
bottom dead center (BDC), and the four strokes of the combustion
cycle (intake, compression, power, and exhaust) is shown in plot
502. Further, a pre-chamber fuel injection signal is shown in plot
504, a pre-chamber air injection signal is shown in plot 506, an
intake valve lift is shown in plot 508, an exhaust valve lift is
shown in dashed plot 510, and a cylinder fuel injection signal is
shown in plot 512. For all of the above, the horizontal axis
represents engine position (e.g., in crank angle degrees), with the
crank angle degrees (CAD) increasing from left to right. The
vertical axis represents each labeled parameter. For plot 502, the
vertical axis shows piston position relative to TDC. For each of
the plots 504, 506, and 512, an increase in magnitude of the
parameter above zero indicates actuation of the corresponding
injector. For plots 508 and 510, the lift of the corresponding
valve increases up the vertical axis from zero. Further, the stroke
of the combustion cycle is indicated at the top of timing chart
500. The power stroke corresponds to an interval from 0 CAD to 180
CAD, the exhaust stroke corresponds to an interval from 180 CAD to
360 CAD, the intake stroke corresponds to an interval from 360 CAD
to 540 CAD, and the compression stroke corresponds to an interval
from 540 CAD to 720 CAD.
[0063] Just prior to the start of the intake stroke (e.g., around
350 CAD), the intake valve is opened (plot 508). As shown in timing
chart 500, an exhaust valve open duration may overlap with an
intake valve open duration, in some examples. For example, after
the start of the intake stroke (e.g., around 380 CAD), the exhaust
valve is closed (dashed plot 510), resulting in positive valve
overlap between the intake valve and the exhaust valve. During the
intake stroke, air is introduced into the cylinder via the intake
valve as the piston (plot 502) moves toward BDC, which is the point
at which the piston is at its bottom-most position in the cylinder
and at the end of the intake stroke (e.g., when the combustion
chamber is at its largest volume).
[0064] At the beginning of the compression stroke (e.g., around 540
CAD), the intake valve closes (plot 508). The piston (plot 502)
moves toward the cylinder head so as to compress the air within the
cylinder. The point at which the piston is at the end of its stroke
and closest to the cylinder head (e.g., when the combustion chamber
is at its smallest volume) is typically referred to as TDC. During
the compression stroke, as the piston (plot 502) moves toward TDC,
a series of injection events may introduce an air-fuel mixture into
the pre-chamber. In the example of FIG. 5, a first air injection
event introduces pre-chamber air (plot 506) into the pre-chamber
while the piston position (plot 502) is relatively low (e.g., while
cylinder pressure is relatively low). Next, a second air injection
event introduces pre-chamber air (plot 506) into the pre-chamber
for combustion while the piston position (plot 502) is higher than
the piston position of the first air injection. Next, as the piston
position further increases, a fuel injection event introduces
pre-chamber fuel (plot 504) into the pre-chamber, which may create
an air-fuel mixture in the pre-chamber. In order to introduce an
air-fuel mixture in the cylinder, a cylinder fuel injection event
introduces an amount of cylinder fuel (plot 512) into the cylinder
before pre-chamber combustion begins at the end of the compression
stroke (e.g., just before 720 CAD).
[0065] As elaborated in the method of FIG. 3, the amount of
cylinder fuel (plot 512) introduced into the cylinder at the end of
the compression stroke may be based on an amount of pre-chamber
gases in the cylinder at the end of the compression stroke. For
example, a controller may increase the amount of cylinder fuel to
compensate for escaped air from the pre-chamber. In another
example, the controller may decrease the amount of cylinder fuel to
compensate for residual combustion gases purged from the
pre-chamber.
[0066] Thus, FIG. 6 shows an exemplary timeline of operating a
cylinder in order to adjust an amount of cylinder fuel based on
amounts of pre-chamber gases according to the method of FIG. 3. The
engine may be engine 10 shown in FIGS. 1, for example, and
controlled by controller 12. An amount of air inducted into the
cylinder is shown in plot 602, an amount of escaped purge air
(e.g., air injected during purging region 406 of FIG. 4 that
escapes to the cylinder) is shown in plot 604, an amount of purged
pre-chamber exhaust is shown in dashed plot 606, a desired cylinder
AFR is shown in plot 608, and a compensated cylinder fuel amount is
shown in plot 610. Further, a stoichiometric AFR is shown by dashed
line 612, and an uncompensated cylinder fuel amount is shown in
dashed plot 614. The uncompensated cylinder fuel amount may
represent a cylinder fuel amount without any correction for
pre-chamber gases in the cylinder. For all of the above, the
horizontal axis represents time, with time increasing along the
horizontal axis from left to right. The vertical axis represents
each labeled parameter. For plots 602, 604, 606, 608, 610, and 612,
a magnitude of the parameter increases up the vertical axis from
top to bottom.
[0067] Prior to time t1, the cylinder operates without a purge
injection in the pre-chamber. As an example, air may be injected
into the pre-chamber only to introduce an air-fuel mixture into the
pre-chamber (e.g., during the injection region 408 of FIG. 4).
Thus, prior to t1, the amount of escaped purge air (plot 604) is
zero, the amount of purged pre-chamber exhaust (dashed plot 606) is
small, and the compensated cylinder fuel amount (plot 610) is
slightly decreased relative to the uncompensated cylinder fuel
amount (dashed plot 614). Because the desired AFR (plot 608) is
stoichiometry (shown by dashed line 612), the cylinder fuel amount
may be a small amount less than the amount of air inducted into the
cylinder (plot 602).
[0068] At time t1, the cylinder begins operating with purge
injections in the pre-chamber, such as shown in FIG. 5, while the
desired cylinder AFR (plot 608) remains at stoichiometry (dashed
line 614) and the amount of air inducted into the cylinder (plot
602) remains constant. For example, during each combustion cycle
after time t1, a first air injection introduces purge air into the
pre-chamber (e.g., during the purging region 406 of FIG. 4).
Further, due to the injection of purge air in the pre-chamber,
residual pre-chamber exhaust gases from a previous combustion cycle
are purged from the pre-chamber into the cylinder. In the example
of FIG. 6, the purged pre-chamber exhaust is assumed to be
fuel-rich. However, in other examples, the purged pre-chamber
residual gases may be stoichiometric, and in still other examples,
the purged pre-chamber residual gases may be lean relative to
stoichiometry. Further, at time t1, the amount of escaped purge air
(plot 604) at time t1 is higher than the amount of purged
pre-chamber exhaust (dashed plot 606) at time t1. Thus, a
composition of the pre-chamber gases includes a higher proportion
of escaped purge air than purged pre-chamber exhaust. In response
to the amount of escaped purge air (plot 604) being higher than the
amount of purged pre-chamber exhaust, the compensated cylinder fuel
amount (plot 610) increases relative to the uncompensated cylinder
fuel amount (dashed plot 614).
[0069] At time t2, the cylinder continues operating with purge
injections in the pre-chamber, while the desired cylinder AFR (plot
608) remains at stoichiometry (dashed line 614) and the amount of
air inducted into the cylinder (plot 602) remains constant.
Further, due to the injection of purging air in the pre-chamber,
residual pre-chamber exhaust gases are purged from the pre-chamber
into the cylinder. However, at t2, the amount of escaped purge air
(plot 604) is lower than the amount of purged pre-chamber exhaust
(dashed plot 606). That is, the composition of the pre-chamber
gases includes a higher proportion of purged pre-chamber exhaust
than escaped purge air. In response to the amount of escaped purge
air (plot 604) being lower than the amount of purged pre-chamber
exhaust, the compensated cylinder fuel amount (plot 610) decreases
relative to the uncompensated cylinder fuel amount (dashed plot
614).
[0070] At time t3, the cylinder continues operating with purge
injections in the pre-chamber, while the desired cylinder AFR (plot
608) remains at stoichiometry (dashed line 614) and the amount of
air inducted into the cylinder (plot 602) increases relative to the
amount of air inducted into the cylinder before time t3. For
example, the amount of air inducted into the cylinder (plot 602)
may increase in response to a change in throttle position or a
change in intake manifold pressure. However, at time t3, the amount
of escaped purge air (plot 604) is higher than the amount of purged
pre-chamber exhaust (dashed plot 606), and so the composition of
the pre-chamber gases includes a higher proportion of escaped purge
air than purged pre-chamber exhaust. In response to the amount of
escaped purge air (plot 604) being higher than the amount of purged
pre-chamber exhaust, and the amount of air inducted into the
cylinder (plot 602) increasing, the compensated cylinder fuel
amount (plot 610) further increases relative to the uncompensated
cylinder fuel amount (dashed plot 614). In particular, the
compensated cylinder fuel amount (plot 610) is higher than the
uncompensated cylinder fuel amount (dashed plot 614) due to the
additional air in the cylinder, both from amount of escaped purge
air (plot 604) and from the amount of air inducted into the
cylinder (plot 602).
[0071] At time t4, the cylinder continues operating with purge
injections in the pre-chamber, while the amount of air inducted
into the cylinder (plot 602) decreases and returns to the amount of
air inducted into the cylinder at t1. However, the desired AFR
(plot 608) decreases relative to stoichiometry (dashed line 612) at
time t4. Thus, the cylinder begins operating with a rich AFR at
time t4. At time t4, the amount of escaped purge air (plot 604) is
higher than the amount of purged pre-chamber exhaust (dashed plot
606). Thus, the composition of the pre-chamber gases includes a
higher proportion of escaped purge air than purged pre-chamber
exhaust. In response to the amount of escaped purge air (plot 604)
being higher than the amount of purged pre-chamber exhaust, and the
desired cylinder AFR (plot 508) decreasing relative to
stoichiometry (dashed line 512), the compensated cylinder fuel
amount (plot 610) increases relative to the uncompensated cylinder
fuel amount (dashed plot 614). In particular, the compensated
cylinder fuel amount (plot 610) is higher than the uncompensated
cylinder fuel amount (dashed plot 614) due to both the additional
air in the cylinder and the decreased (e.g., enriched) desired
cylinder AFR (plot 608).
[0072] In this way, a cylinder with a pre-chamber ignition system
may be operated to provide torque to an engine by combusting an
air-fuel mixture, and a cylinder fuel amount may be adjusted to
compensate for pre-chamber gases in the cylinder prior to
combustion. For example, a controller may determine amounts of
pre-chamber gases, including air and residual exhaust gas, based on
a pressure in the cylinder and geometric properties of the
pre-chamber. Further, the controller may determine the cylinder
fuel amount based on an amount of purge air, an amount of purged
exhaust gas from the pre-chamber, and an amount of air inducted
into the cylinder. As a result, the cylinder fuel amount is
compensated for the pre-chamber gases in order to achieve a desired
AFR in the cylinder. Adjusting cylinder fueling for pre-chamber
gases may increase a fuel efficiency of the cylinder and may
increase a combustion stability of the cylinder. Overall,
compensating cylinder fueling for amounts of pre-chamber gases in
the cylinder may increase customer satisfaction relative to engine
systems with uncompensated cylinder fueling.
[0073] The technical effect of adjusting cylinder fueling based on
amounts of pre-chamber gases in the cylinder is that a desired
air-fuel ratio may be more accurately achieved in the cylinder,
thereby decreasing vehicle emissions that may otherwise result from
inaccurate air-fuel ratio control.
[0074] As one example, a method comprises: adjusting a fuel
injection amount to a cylinder based on an amount of pre-chamber
gases in the cylinder during a compression stroke of the cylinder.
In the preceding example, additionally or optionally, the
pre-chamber gases flow to the cylinder from a pre-chamber coupled
to the cylinder via an opening in walls of the pre-chamber. In one
or both of the preceding examples, additionally or optionally, the
amount of pre-chamber gases is determined based on a pressure
difference between the pre-chamber and the cylinder. In any or all
of the preceding examples, additionally or optionally, the pressure
difference between the pre-chamber and the cylinder is determined
based on an injection pressure of the pre-chamber and a position of
a piston within the cylinder. In any or all of the preceding
examples, additionally or optionally, the injection pressure of the
pre-chamber is greater than or equal to a peak pressure of the
cylinder. In any or all of the preceding examples, additionally or
optionally, the amount of pre-chamber gases includes one or more of
an amount of pre-chamber air, an amount of pre-chamber fuel, and an
amount of pre-chamber combustion gases from a previous combustion
cycle. In any or all of the preceding examples, additionally or
optionally, adjusting the fuel injection amount to the cylinder
includes increasing the fuel injection amount to the cylinder as
the amount of pre-chamber air in the cylinder during the
compression stroke increases. In any or all of the preceding
examples, additionally or optionally, adjusting the fuel injection
amount to the cylinder includes decreasing the fuel injection
amount to the cylinder as the amount of pre-chamber fuel in the
cylinder during the compression stroke increases. In any or all of
the preceding examples, additionally or optionally, adjusting the
fuel injection amount to the cylinder includes decreasing the fuel
injection amount to the cylinder as the amount of pre-chamber
combustion gases from the previous combustion cycle in the cylinder
during the compression stroke increases. In any or all of the
preceding examples, additionally or optionally, adjusting the fuel
injection amount to the cylinder is further based on an amount of
air inducted into the cylinder through an intake valve of the
cylinder.
[0075] As another example, a method comprises: determining an
amount of gases purged from a pre-chamber to a cylinder based on a
pressure difference between the pre-chamber and the cylinder during
purging; and adjusting fueling to the cylinder based on the amount
of gases purged from the pre-chamber to the cylinder. In the
preceding example, the method additionally or optionally further
comprises determining a composition of the gases purged from the
pre-chamber to the cylinder based in part on parameters of a
previous pre-chamber combustion event, and the purging includes
actuating an air injector of the pre-chamber during a compression
stroke of the cylinder. In one or both of the preceding examples,
additionally or optionally, the composition includes at least one
of pre-chamber air, pre-chamber fuel, and pre-chamber exhaust gas,
and adjusting the fueling to the cylinder includes: increasing the
fueling to the cylinder as an amount of pre-chamber air increases;
decreasing the fueling to the cylinder as an amount of pre-chamber
fuel increases; and decreasing the fueling to the cylinder as an
amount of pre-chamber exhaust gas increases. In any or all of the
preceding examples, additionally or optionally, the parameters of
the previous pre-chamber combustion event include a pre-chamber
fuel injection pressure, a pre-chamber fuel injection amount, a
pre-chamber air injection pressure, a pre-chamber air injection
amount, and a pre-chamber spark timing. In any or all of the
preceding examples, additionally or optionally, the pressure
difference between the pre-chamber and the cylinder during the
purging is determined based on an injection pressure of an air
injector of the pre-chamber and a piston position of the cylinder,
and the injection pressure of the air injector is at least equal to
a peak pressure of the cylinder.
[0076] As another example, a system comprises: an engine including
a plurality of cylinders, each cylinder including a cylinder fuel
injector and a pre-chamber of a pre-chamber ignition system; and a
controller storing executable instructions in non-transitory memory
that, when executed, cause the controller to: purge gases from the
pre-chamber to the corresponding cylinder; and adjust a fuel
injection amount of the cylinder fuel injector based on an amount
and composition of the gases purged from the pre-chamber. In the
preceding example, additionally or optionally, the pre-chamber
includes an air injector, a pre-chamber fuel injector, and a spark
plug, and the composition of the gases purged from the pre-chamber
includes at least one of air, fuel, and exhaust gas from a previous
combustion in the pre-chamber. In one or both of the preceding
examples, additionally or optionally, to adjust the fuel injection
amount of the cylinder fuel injector based on the amount and
composition of the gases, the controller includes further
instructions stored in non-transitory memory that, when executed,
cause the controller to: increase the fuel injection amount of the
cylinder fuel injector as a proportion of air in the gases purged
from the pre-chamber increases; decrease the fuel injection amount
of the cylinder fuel injector as a proportion of fuel in the gases
purged from the pre-chamber increases; and decrease the fuel
injection amount of the cylinder fuel injector as a proportion of
exhaust gas from the previous combustion in the pre-chamber in the
gases purged from the pre-chamber increases. In any or all of the
preceding examples, additionally or optionally, to purge gases from
the pre-chamber to the corresponding cylinder, the controller
includes further instructions stored in non-transitory memory that,
when executed, cause the controller to: actuate the air injector
during a compression stroke of the cylinder at an injection
pressure at or above a peak pressure of the cylinder. In any or all
of the preceding examples, additionally or optionally, the
controller includes further instructions stored in non-transitory
memory that, when executed, cause the controller to: determine the
peak pressure of the cylinder based on at least a temperature of
the engine and engine load.
[0077] As another representation, a method comprises: adjusting an
injection pressure of a one or more pre-chamber injectors based on
a peak pressure of a cylinder during a compression stroke of the
cylinder. In the preceding example, additionally or optionally, the
one or more pre-chamber injectors include an air injector, and
adjusting the injection pressure includes increasing the injection
pressure of the air injector above the peak pressure of the
cylinder. In one or both of the preceding examples, additionally or
optionally, the one or more pre-chamber injectors include a
pre-chamber fuel injector, and adjusting the injection pressure
includes increasing the injection pressure of the pre-chamber fuel
injector above the peak pressure of the cylinder. In any or all of
the preceding examples, additionally or optionally, the peak
pressure of the cylinder is determined based on an amount of air in
the cylinder during the compression stroke and a volume of the
cylinder when a piston within the cylinder reaches top dead center
of the compression stroke. In any or all of the preceding examples,
additionally or optionally, the amount of air in the cylinder is
determined based on an intake manifold pressure. In any or all of
the preceding examples, additionally or optionally, the amount of
air in the cylinder is determined based on a throttle position. In
any or all of the preceding examples, the method additionally or
optionally further comprises: performing a first injection with the
air injector at the injection pressure above the peak pressure of
the cylinder during a first portion of the compression stroke, when
the piston in the cylinder is lower; performing a second injection
with the air injector at the injection pressure above the peak
pressure of the cylinder during a second portion of the compression
stroke, when the piston in the cylinder is higher; and performing a
fuel injection with the pre-chamber fuel injector at the injection
pressure above the peak pressure of the cylinder during the second
portion of the compression stroke. In any or all of the preceding
examples, the method additionally or optionally further comprises:
adjusting an amount of fuel injected into the cylinder based on an
amount and composition of pre-chamber gases in the cylinder during
the compression stroke. In any or all of the preceding examples,
additionally or optionally, the amount and composition of the
pre-chamber gases in the cylinder during the compression stroke are
determined in part based on the injection pressure of the air
injector and the injection pressure of the pre-chamber fuel
injector.
[0078] Note that the example control and estimation routines
included herein can be used with various engine and/or vehicle
system configurations. The control methods and routines disclosed
herein may be stored as executable instructions in non-transitory
memory and may be carried out by the control system including the
controller in combination with the various sensors, actuators, and
other engine hardware. The specific routines described herein may
represent one or more of any number of processing strategies such
as event-driven, interrupt-driven, multi-tasking, multi-threading,
and the like. As such, various actions, operations, and/or
functions illustrated may be performed in the sequence illustrated,
in parallel, or in some cases omitted. Likewise, the order of
processing is not necessarily required to achieve the features and
advantages of the example embodiments described herein, but is
provided for ease of illustration and description. One or more of
the illustrated actions, operations, and/or functions may be
repeatedly performed depending on the particular strategy being
used. Further, the described actions, operations, and/or functions
may graphically represent code to be programmed into non-transitory
memory of the computer readable storage medium in the engine
control system, where the described actions are carried out by
executing the instructions in a system including the various engine
hardware components in combination with the electronic
controller.
[0079] It will be appreciated that the configurations and routines
disclosed herein are exemplary in nature, and that these specific
embodiments are not to be considered in a limiting sense, because
numerous variations are possible. For example, the above technology
can be applied to V-6, 1-4, I-6, V-12, opposed 4, and other engine
types. The subject matter of the present disclosure includes all
novel and non-obvious combinations and sub-combinations of the
various systems and configurations, and other features, functions,
and/or properties disclosed herein.
[0080] As used herein, the term "approximately" is construed to
mean plus or minus five percent of the range unless otherwise
specified.
[0081] The following claims particularly point out certain
combinations and sub-combinations regarded as novel and
non-obvious. These claims may refer to "an" element or "a first"
element or the equivalent thereof. Such claims should be understood
to include incorporation of one or more such elements, neither
requiring nor excluding two or more such elements. Other
combinations and sub-combinations of the disclosed features,
functions, elements, and/or properties may be claimed through
amendment of the present claims or through presentation of new
claims in this or a related application. Such claims, whether
broader, narrower, equal, or different in scope to the original
claims, also are regarded as included within the subject matter of
the present disclosure.
* * * * *